tools: ynl: fix build on systems with old kernel headers

The wireguard YNL conversion was missing the customary .deps entry.
NIPA doesn't catch this but my CentOS 9 system complains:

wireguard-user.c:72:10: error: ‘WGALLOWEDIP_A_FLAGS’ undeclared here
wireguard-user.c:58:67: error: parameter 1 (‘value’) has incomplete type
58 | const char *wireguard_wgallowedip_flags_str(enum wgallowedip_flag value)
| ~~~~~~~~~~~~~~~~~~~~~~^~~~~

And similarly does Ubuntu 22.04.

One extra complication here is that we renamed the header guard,
so we need to compat with both old and new guard define.

Reviewed-by: Asbjørn Sloth Tønnesen <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

tools/net/ynl/Makefile.deps

···
 # need the explicit -D matching what's in /usr, to avoid multiple definitions.
 
 get_hdr_inc=-D$(1) -include $(UAPI_PATH)/linux/$(2)
+get_hdr_inc2=-D$(1) -D$(2) -include $(UAPI_PATH)/linux/$(3)
 
 CFLAGS_devlink:=$(call get_hdr_inc,_LINUX_DEVLINK_H_,devlink.h)
 CFLAGS_dpll:=$(call get_hdr_inc,_LINUX_DPLL_H,dpll.h)
···
 	$(call get_hdr_inc,_TC_SKBEDIT_H,tc_act/tc_skbedit.h) \
 	$(call get_hdr_inc,_TC_TUNNEL_KEY_H,tc_act/tc_tunnel_key.h)
 CFLAGS_tcp_metrics:=$(call get_hdr_inc,_LINUX_TCP_METRICS_H,tcp_metrics.h)
+CFLAGS_wireguard:=$(call get_hdr_inc2,_LINUX_WIREGUARD_H,_WG_UAPI_WIREGUARD_H,wireguard.h)